Field of the Invention
The present invention relates to a technique for inspecting a spatial light modulator.
Description of the Background Art
A GLV (Grating Light Valve) (registered trademark of Silicon Light Machines (San Jose, Calif.)) which is a ribbon diffracting element is known as a spatial light modulator. Referring to the GLV, a modulating element is formed by a fixed reflecting surface and a movable reflecting surface with respect to a fixed surface, and a plurality of modulating units are arranged in a predetermined direction. In the case where the GLV is used, uniformity of light reflected from the GLV greatly affects an exposure result. For this reason, in a drawing device using the GLV, it is indispensable to adjust an amount of light reflected from the GLV. In recent drawing devices, particularly, an enhancement in fineness of drawing is required and an enhancement in fineness of adjustment of the amount of reflected light is also demanded.
Referring to the GLV, a voltage is applied to a movable ribbon configuring the movable reflecting surface in each modulating unit so that the movable reflecting surface is moved to a recessed position with respect to the fixed reflecting surface. A size of the recessed part can be regulated depending on an amount of the voltage to be applied, and light incident on each modulating unit is switched into zero order light and diffracted light in order other than zero order so that the amount of the light reflected from the modulating unit can be controlled. When the GLV is attached to the drawing device, a relationship (hereinafter referred to as an “IV characteristic”) between an amount of reflected light (I) and an amount of a voltage (V) is analyzed for each modulating unit. Based on a result of the analysis, the amount of the light reflected from each modulating unit is controlled.
The related art relating to the present invention is described in Japanese Patent Application Laid-Open No. 2014-106513, for example.
In general, a great load is applied to the GLV because a high power laser beam is radiated thereon. For this reason, it is known that each modulating unit is deteriorated with an increase in an operating time of the GLV and the amount of the reflected light fluctuates with respect to an equal voltage. Therefore, it is necessary to periodically reacquire IV characteristic information of the modulating unit. However, respective modulating units have different characteristics from each other, and furthermore, times required for exposure to the laser beam are also different from each other. For this reason, the IV characteristic information should be acquired for each modulating unit. In the case where the number of the modulating units is large, accordingly, a labor and time is greatly required for reacquiring the IV characteristic information.
Moreover, there is no effective index for quantitatively grasping a degree of deterioration from an initial state for each modulating unit of the GLV. For this reason, it is hard to grasp which modulating unit is deteriorated or to what degree the modulating unit is deteriorated.